The transmit/receive (T/R) switch is, a crucial functional block in a radio frequency (RF) transceiver front-end, which generally includes one transmission branch and one reception branch. Along the reception branch, the received RF signals will be passed through a bandpass filter (BPF) and then switched by a T/R switch to a low-noise amplifier (LNA); while in the transmission branch, the transmitted RF signals will be amplified by a power amplifier (PA), and then switched by the T/R switch to the antenna. In particular, a T/R switch can be found in any time-division duplexing (TDD)-based radio front-end, and it connects radio transmitter (TX) and receiver (RX) alternatively to a shared antenna (ANT). A TDD radio system can inherently offer a number of advantages and flexibilities that a frequency-division duplexing (FDD) radio system cannot. These advantages include channel reciprocity, dynamic bandwidth allocation, and higher frequency diversity. TDD is dominant in 3G, 4G LTE/WiMAX, Bluetooth, WLAN, UWB and 60 GHz radio systems and is expanding its share in cellular radio systems.
Many switches have been implemented to address the particular performance parameters. To achieve low insertion loss, most of the switches are implemented by monolithic microwave integrated circuits with traveling wave techniques and discrete active components such as PIN diodes and gallium arsenide (GaAs) pseudomorphic high-electron-mobility transistors (PHEMTs), especially at high frequencies. For example, transmission lines, stubs and PIN diodes may be adopted to realize discrete TDD T/R switch. Prior art switches may use PIN diodes to implement low insertion loss switches. However, these types of switches are too bulky to be integrated on-chip with the entire transceiver. In addition, the cost of the process used is high.
T/R switches using a series-shunt topology with CMOS (complementary metal-oxide-semiconductor) process have also been proposed, owing to the low cost and high integration ability of the CMOS process. Floating bulk is also used in MOSFET transistors of the switches to reduce the effects of parasitic diodes, leading to enhanced linearity and power handling ability. However, due to the limitation of the CMOS process and circuit topology, their operating bandwidth is limited to low-giga-hertz applications. For high frequency applications, the traveling wave concept is used commonly to extend the operating frequency. Nevertheless, for an operating frequency above 50 GHz, switches are mostly dominated by GaAs switches.